Use composition over inheritance for Lotus::Utils::Callbacks::Chain

Before:

  irb(main):001:0> require 'lotus/utils/callbacks'
  => true
  irb(main):002:0> Lotus::Utils::Callbacks::Chain.new.methods.size
  => 173

After:

  irb(main):001:0> require 'lotus/utils/callbacks'
  => true
  irb(main):002:0> Lotus::Utils::Callbacks::Chain.new.methods.size
  => 58
  irb(main):003:0> Object.new.methods.size
  => 56